I do not have this camera myself, however I did some searching on the Argus website. While they did not specifically state how to set the camera to use the SD card as the main storage for your photos, I can give you a few pointers.
It seems that the camera will automatically use the SD card to store pictures when it is inserted.
Did the camera ask you to format the SD card when you inserted it into the camera? If so, that means that it at least recognizes that it is there. On the other hand, if it did not ask you, then it is possible that the card was already formatted and is ready to use.
I would try taking some pictures, say 15-20, to test it out. If it tells you that it ran out of memory, then the card is not being used and you are back to square one.
Below is the website for your camera where you will find the manual and the drivers for the camera if you decide to connect it to your computer. Also, I have included the support phone number in case if you are still having trouble.http://www.arguscamera.com/products/qc3185.htm
Argus Tech Support: